Recent work in our laboratory has shown that the mRNAs coding for two muscle-specific proteins, actin and myosin heavy chain, are present in embryonic skeletal muscle cells as cytoplasmic messenger ribonucleoprotein (mRNP) particles. Such particles have been implicated in the regulation of myogenesis of skeletal muscle cells in culture. The aim of this project is the elucidation of the molecular mechanisms involved in the regulation of myogenesis. We plan to carry out studies along several specific lines: (1) quantitative estimation of the muscle-specific mRNAs at various stages of growth and differentiation of the embryonic muscle cells, and (2) the possible role of translational control, if any, in these processes. These studies will be complemented by investigating whether or not cytoplasmic mRNP particles are also involved in the regulation of translation in muscle cells at a cytoplasmic level. It is hoped that the results of these studies will be helpful in understanding the molecular basis of the regulation of myogenesis and in probing for possible alterations of such regulatory mechanisms in pathological states of the muscle tissue such as a muscular dystrophy and cardiac hypertrophy. BIBLIOGRAPHIC REFERENCES: Roy, R.K., Sreter, F.A. and Sarkar, S., Tropomyosin Subunits in Avian and Mammalian Muscles: Differences in Gene Expression in Adult and Embryonic Fibers, Fed. Proc. 36, 1977. Sarkar, S., and Bag, J., Release of mRNA-associated Proteins During In Vitro Translation of Cytoplasmic mRNP Particles of Chick Embryonic Muscles, Fed. Proc. 36, 1977.